HTTPS env var should be "on" when using mod_extforward and the X-Forwarded-Proto header is set.

mod_extforward should parse the "X-Forwarded-Proto" header. If it is equal to "https", this should be stored in the connection variable somewhere (i.e. the is_ssl variable should be set to 1). However, simply setting is_ssl to 1 breaks the server, so there should be another way to make mod_fastcgi set the HTTPS environment variable.